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YOUR FORM TO THE ABOVE ADDRESS. 1. REPORT DATE (DD-MM-YYYY) August
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4. TITLE AND SUBTITLE Hansen Solubility Parameters for
Fluoroalkylsilicates
5a. CONTRACT NUMBER In-House
5b. GRANT NUMBER
5c. PROGRAM ELEMENT NUMBER
6. AUTHOR(S) 5d. PROJECT NUMBER
Andrew Guenthner, Timothy Haddad, Kevin Lamison, Gregory Yandek,
Lisa Lubin, Joseph Mabry
5e. TASK NUMBER
5f. WORK UNIT NUMBER Q0BG
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Air Force Research Laboratory (AFMC) AFRL/RQRP 10 E. Saturn
Blvd. Edwards AFB CA 93524-7680
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SPONSOR/MONITOR’S ACRONYM(S)Air Force Research Laboratory (AFMC)
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93524-7048 NUMBER(S) AFRL-RQ-ED-VG-2012-281
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13. SUPPLEMENTARY NOTES Briefing Charts for the Fluoropolymer
2012, Las Vegas, Nevada in 17 October 2012.
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Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std. 239.18
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HANSEN SOLUBILITY PARAMETERS FOR FLUOROALKYL SILICATES
October 17, 2012
Andrew Guenthner1*, Gregory R. Yandek1, Timothy S. Haddad2,
Kevin R. Lamison2, Lisa M. Lubin3, Joseph M. Mabry1 1Aerospace
Systems Directorate, Air Force Research Laboratory
2ERC Corporation 3 AFRL Summer Externship Program
[email protected] Approved for public release;
distribution is unlimited..
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Outline • Background / Motivation
– Fluoro-POSS Applications as Polymer Modifiers – Relationships
Between Surface and Bulk Energy
• Hansen Solubility Parameters for Bulk Energy • Girifalco-Good
Parameters for Surface Energy
• Previous Work on Fluoro-POSS Surface Energy • Current Work on
Fluoro-POSS Bulk Energy
– HSP of Fluoro-POSS and Related Silicate Compounds – Group
Contribution Estimates
• Comparisons of Surface and Bulk Energy Values
Acknowledgements: Air Force Office of Scientific Research, Air
Force Research Laboratory – Program Support; PWG team members
(AFRL/RQRP) and Collaborators (MIT – Profs. Robert Cohen and Gareth
McKinley; Univ. Mich – Prof. Anish Tuteja; Clemson/AFA – Dr. Scott
Iacono; Clemson/UT Dallas – Prof. Dennis Smith
2
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128° 88°
Effect of Fluorodecyl-POSS on Poly-(chlorotritluoroethylene )
Surfaces
Hexadecane Contact Angles
0
10
20
30
40
50
60
70
No POSS 5% FO 10% FO 5% FD 10% FD
Weight Percent POSS
Cont
act A
ngle
40°
27° 31°
58°
No POSS 10 wt% POSS Water Contact Angles …
Significant improvements in repellence of both water and oil are
seen when fluoro-POSS is added to PCTFE
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121º 95º
31º 80º
Water
Hexadecane
Water
Hexadecane
26°
49°
10% FD POSS in 6F PFCB polymer
No POSS 10 wt% POSS
Another example of a fluoropolymer with liquid repellence
improved by addition of fluoro-POSS, presumably due to the lower
surface energy of Fluoro-POSS
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95º (H2O) 31º (Oil)
15 wt% FD8T8 6F PFCB
0.5 nm rms
121º (H2O) 80º (Oil)
1.5 nm rms
Water Water
EDX/AFM of POSS/PFCB Surfaces Composite Blend
5
EDX shows that the surface becomes enriched in fluoro-POSS; AFM
shows that surface migration alters the surface topography in
addition to lowering surface energy.
5
The performance of fluoropolymers with added fluoro-POSS depends
on both bulk (phase separation) and surface (migration)
energies.
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POSS/PMMA: Spin coating smooth surfaces
160
140
120
100
80
60
Con
tact
Ang
le (°
)
0.60.50.40.30.20.10.0Mass Fraction Fluorodecyl POSS
Advancing contact angleReceding contact angle
6
Pure PMMA is hydrophilic, yet phase separation and surface
migration drastically alter water repellence. Understanding both
bulk and surface interactions between fluoro-POSS and polymers is
the key to controlling performance. At present, a quantitative
understanding of these phenomena is lacking.
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Controlled Surface Repellence Is an Important Enabler for AF
Applications
7
Helicopter vortex tubes are used to exclude dust and
contaminants from engine intakes. Requirements include light
weight, ease of manufacturing, mechanical (structural / abrasion
resistance), fouling resistance, and thermal performance.
The traditional material is a polypropylene that is highly
filled to provide the required performance. The high filler loading
makes manufacturing difficult due to the low thickness of part
features (needed to save weight) that must be molded using a high
viscosity material.
Inert POSS compounds, added as flow aids, allow more robust
plastics such as cyclic olefin copolymers (COCs) to replace the
polypropylene base material without sacrificing the ease of flow
that facilitates ease of manufacturing. The high thermal stability
and ~1 nm size of the POSS molecules provide the best available
flow-enhancing characteristics and could also aid fouling
resistance.
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Bulk Interactions Can Be Quantified through Hansen Solubility
Parameters
• Hansen parameters developed in late 1960s / early 1970s
enabled development of a solvent mixture (n-butanol / nitroethane)
for removal of “insoluble” epoxy primers from metal surfaces
• Hansen Solubility Parameters became widely used in the
coatings industry, including for systems containing inorganic
pigments – they remain the only successful approach for achieving
miscibility via mixed solvents
• Solubility parameters for POSS compounds studied since ~2010
by numerous groups (Morgan-USM, Schiraldi-CWRU, AFRL)
8
•
•
•
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Relation Between HSP and Phase Separation Dynamics
Hmix = 1 2 Vref[( D1 – D2)2 + (1/4) ( P1 - P2)2 + (1/4)( H1 -
H2)2]
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Knowledge of Hansen Solubility Parameters enables the
computation of the enthalpy of mixing between two components. For
polymers, the value of the enthalpy of mixing controls the rate and
extent of phase separation. When plotted in a 3-dimensional
“solubility parameter space”, good solvents (an indication of low
enthalpy of mixing) tend to lie within a “sphere of solubility”
centered on co-ordinates that correspond to the HSP of the solute.
This “spherical rule” results from the similarity of the above
equation to a geometric distance formula.
2 = D2 + P2 + H2
Hansen Solubility Parameter diagram for CO2
2 = (ΔHvap – RT) / V Enthalpy of mixing
Solubility parameter Dispersive, polar, and H-bonding components
Molar volume
Volume fractions
Molar enthalpy of vaporization
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Hansen Solubility Parameters for Polymer Systems
Source: Hansen Solubility Parameters: A User’s Handbook, 2nd
ed., CRC Press, 2007
Experimental method for determining HSP
1. Determine solubility (or affinity) in a large set of trial
solvents
2. Plot the HSP of “good” and “poor” solvents in a “solubility
parameter space” as shown.
3. “Good” solvents normally lie near one another in a “region of
solubility”
4. When 2 D is used as an axis, the region of solubility is
typically bounded by a sphere.
5. The center coordinates of the sphere mark the newly
determined HSP.
6. With knowledge of the HSP and “radius of interaction” (test
dependent), test results for any subsequent solvent (or mixture)
are reliably predicted.
2 D
H
P
The traditional approach to estimating Hansen solubility
parameters requires trials of typically 30 or 50 different
solvents, but is straightforward to carry out. “Good” typically is
indicated by >5% or 10% solubility, or by swelling, ESC,
etc.
Solubility sphere
Solubility parameter space Hansen solubility
parameters (HSP)
“Good” solvent
“Poor” solvent
Region of solubility
Radius of interaction
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Quantitative Interaction Parameters for Surfaces: Girifalco-Good
Approach
• Measurement of contact angles for several probe liquids is
used to determine the component values using linear regression.
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Work of adhesion between solid and liquid
Equilibrium contact angle
Dispersive components
Acid (+) / base (-) component interaction terms
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Relationships Between Surface and Bulk Properties
• These relationships predict the properties of liquid surfaces,
however, most fluorosilicates are solids at room temperature
• Even in liquids, molecular order at the surface is not taken
into account by the predicted values
• To date, no widely known correlations exist for polar and
hydrogen bonding components
• In general, hydrogen bonding is much stronger in bulk than at
the surface (perhaps due to fewer constraints on interlocking in
the bulk)
γD = 4.79 D - 51.87
γ = 0.75 4/3
γ = [ Ps / V(T) ]4; Ps ~ Vw
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D. W. Van Krevelen, Properties of Polymers, 3rd ed., (Elsevier,
Amsterdam, 1990)
M. Bicerano, Prediction of Polymer Properties, 3rd ed. (Marcel
Dekker, New York, 2002)
A. Carré and J. Vial, J. Adhesion, 1995, 42, 265.
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Fluoro-POSS and Related Fluoro- alkyl Silicate Compounds
• T and Q compounds are crystalline at room temperature • M
compound is liquid at room temperature • Q compound can be thought
of as roughly half a POSS cage; M
compound as roughly one-fourth a POSS cage
HSP GG
13
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HSP Data for Fluoroalkyl Silicate Compounds
Octa-hexafluoroisobutyl-POSS
Octa-trifluoropropyl-POSS
Octa-fluorohexyl-POSS
Fluorodecyl-M2
H H
H H
D D
D D P
P
P
14
P
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Comparison of Hansen Solubility Parameters for POSS
Compounds
HSP trends do reflect the qualitative features expected on the
basis on the peripheral chemical structure, such as: • Smaller D
for fluorocarbons • Larger P for fluorocarbons
HSP for multiple POSS types provide an estimate of the HSP for a
T8 cage
POSS / Silicate Type D P H R0 #Exceptions / #Good
Octa-isobutyl 18.0 2.1 2.7 4.5 6 / 8
Octa-hexafluoroisobutyl 15.3 9.3 11.0 7.3 2 / 10
Octa-fluorohexyl 16.3* 6.8* 6.7* 2* n/a
Octa-trifluoropropyl 16.8 9.1 8.9 4.5 0 / 5
Fluorodecyl-M2 16.0* 5.4* 5.3* 5* n/a All units (J/cc)1/2
T8 POSS cage
15 *estimated
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Comparison of Surface Energy Parameters for POSS Compounds
Predicted values based on Hansen Solubiliy Parameters (for
“liquid” surfaces) γlv (dyn / cm) γdlv (dyn / cm) Fluorodecyl T8
34.6 24.8 Fluorohexyl T8 37.7 26.2 Fluoropropyl T8 43.7 28.6
Hexafluoroi-i-butyl T8 43.5 21.4 Fluorodecyl M2 34.6 24.8 • For
perfluoroheptane, the predicted value of γlv of 21 dyn/cm is close
to expectations • Agreement for the dispersive component is better,
but γdlv < γlv without rearrangement 16
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Application to Miscibility and Phase Separation
The Time-Dependent Ginzburg-Landau equation (linearized to
Cahn-Hilliard equation) represents the established mathematical
framework for predicting phase separation, if you know the “ ”
parameter
2, ,r t GM r tt
= Vref[( D1 – D2)2 + (1/4) ( P1 - P2)2 +
(1/4)( H1 - H2)2] As an example, for octa-phenethyl-POSS in PEI:
Phenethyl-POSS: (J/cc)1/2
D = 19.7; P2 = 8.0 H = 5.6;
PEI: (J/cc)1/2 D
= 19.6; P2 = 7.6 H = 9.0; Vref = 100 cc/mol = 0.12 N1 = 10; N2 =
100 Predicted miscibility: 10-20% Actual miscibility: 2.6%
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Surface Migration of 5 wt% Octa- Phenethyl POSS in PEI
1 hr @ 180°C 2 hrs @ 180°C
1 hr @ 210°C 2 hrs @ 210°C
0 nm 50 nm Surface Height Map
Films annealed at 180°C show effects that are not significantly
different from those seen in pure PEI. At 210°C, fine aggregates
and, later, a phase separated texture appear. The insets show the
autocovariance (same length scale as main figure, red = high) of
the pattern for annealing at 210°C, indicating periodicity. 20
m
20 m 20 m
20 m
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Future Work
• Determine Hansen solubility parameters for additional silicate
types (“D”
is available from polysiloxanes, “T” from POSS, more “M” and “Q”
examples needed)
• Improve precision of group contribution values for POSS cages
and other silicate structures, as well as for fluorocarbons
• Generate additional predictions of miscibility and develop a
spatio-temporal model for surface migration of silicate
additives
• Use controlled migration to design organic / inorganic hybrids
with optimal liquid repellence and other desirable properties
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Summary
• Controlling the liquid repellence characteristics of polymer /
silicate nanocomposites requires quantitative knowledge of both
bulk and surface thermodynamic parameters.
• Quantitative surface and bulk thermodynamic data for polymer /
silicate nanocomposites (including fluorinated polymers and
fluoro-POSS) has recently become available.
• Comparisons of surface and bulk thermodynamic parameters
provide insight into the nature of the silicate / polymer
nanocomposite surface
• Application of the thermodynamic data to investigate
miscibility and phase separation in polymer / silicate
nanocomposites is underway
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